1. Field of the Invention
The present invention relates to a base material for forming a single crystal diamond and a method for producing a single crystal diamond using the base material.
2. Description of the Related Art
Diamond has a wide band gap of 5.47 eV and a very high dielectric breakdown electric field intensity of 10 MV/cm. Furthermore, it has the highest thermal conductivity in materials. Therefore, if this is used for an electronic device, the device is advantageous as a high output electronic device.
Furthermore, diamond has a high drift mobility and is the most advantageous as a high speed electronic device in semiconductors in comparison of Johnson performance index.
Accordingly, diamond is said to be the ultimate semiconductor suitable for high frequency/high power electronic devices.
Therefore, studies of various kinds of electronic devices using a single crystal diamond for a base material has progressed.
Now, the single crystal diamonds for fabrication of a diamond semiconductor are diamonds referred to as Ib type formed by a high-pressure-high-temperature method (HPHT) or IIa type of which purity is enhanced.
However, it is difficult to grow in size while the HPHT method can provide the diamond having a high crystallinity. In addition, a price of the diamond becomes extremely high when its size becomes big. Therefore, it is difficult to put into practical use as a base material for the devices.
Therefore, a CVD single crystal diamond formed by a vapor deposition method is also studied to provide a low cost base material having a large area.
Recently, a homoepitaxial CVD single crystal diamond that is homoepitaxially grown on the HPHT single crystal diamond base material directly by the vapor deposition method was reported (the 20th diamond symposium lecture summary (2006), pp. 6-7).
In this method, since the base material and the single crystal diamond grown use the same material, it is difficult to separate these. Therefore, there are cost problems that, for example, the base material needs implanting ions in advance and a lengthy wet etching separation treatment after growth. Moreover, there is another problem that crystallinity of the single crystal diamond to be obtained deteriorates to a certain degree due to ion implantation of the base material.
As an alternative, a heteroepitaxial CVD single crystal diamond heteroepitaxially grown by a CVD method on a single crystal iridium heteroepitaxially grown on a single crystal MgO was reported (Jpn. J. Appl. Phys. Vol. 35 (1996), pp. 1072-1074).
However, in this method, there is a problem that the base material and the single crystal diamond grown are finely broken due to stress generated between the single crystal MgO and the single crystal diamond grown via the single crystal iridium (sum of internal stress and heat stress). Moreover, crystallinity of the single crystal diamond to be obtained does not achieve a satisfactory level since crystallinity of an available single crystal MgO that is a seed base material is not sufficient.